The present invention relates generally to control valves and more particularly relates to control valves particularly adapted for controlling the displacement of a main drive pump and hydrostatic transmission.
In the above-mentioned copending application Ser. No. 610,234 there is disclosed a hydrostatic transmission which is controlled by controlling the amount and pressure of fluid at the inlet of the drive pump. The control valve disclosed therein will control the quantity of fluid flowing to the pump during periods of low speed operation of the transmission and will control the pressure of the fluid flowing to the pump during periods of high speed operation. The control valve disclosed in the aforementioned copending application provides extremely good control characteristics, but requires a varying, often high effort to move the control plunger and in the event of a failure in the mechanical control linkage for the valve, the valve can move to and remain in its fully open position so that the transmission continues to operate at high speeds.